The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Virtual Private Network (VPN) is a technology that relies on Internet Service Provider (ISP) and Network Service Provider (NSP) to establish a private data communication network in a public network. The VPN can be categorized into Layer-2 VPN (L2VPN) and Layer-3 VPN (L3VPN), etc.
The L2VPN provides a layer-2 VPN service based on Packet Switched Network, such as MultiProtocol Label Switching (MPLS) network.
FIG. 1 illustrates a conventional networking schematic for L2VPN. A Customer Edge (CE) device has an interface to connect to the ISP network directly. PE is an edge device in ISP network, connecting directly to CE device. Service Provider (P) is a backbone router in ISP network. It does not connect to CE directly. In FIG. 1, a Label Switching Path (LSP) is a unidirectional virtual connection between two PEs. A Pseudo Wire (PW) is a bidirectional virtual connection between two PEs, transmitting frames between two PEs. PE utilizes signaling to set up and maintain PW. The status information of a PW is maintained by PEs located at two ends of the PW.
In a related art, there are two approaches to detect a fault of the PW in L2VPN.
One is to employ a conventional Bidirectional Forwarding Detection (BFD) technique or an MPLS Operation Administration and Maintenance (MPLS OAM) to detect a fault of the PW. However, when the number of PWs is large, devices will be overloaded when operating BFD or MPLS OAM. Moreover, the messages sent for BFD or MPLS OAM may take up a huge amount of network bandwidth. Consequently, the shortcoming of this approach is that when the number of PWs is large, the processing overhead of the device and the network bandwidth occupation is huge.
Another approach is to detect a fault of the LSP first, using BFD or MPLS OAM. The detection result is then used for detection of a fault of the PW. However, in this approach, since it can not be ascertained which PW is associated with LSP after a fault of the LSP is detected, this approach is not able to detect fault of the PW correctly. As an example, FIG. 2 illustrates relationship between PWs and LSPs. CE1, CE2, CE3 and CE4 all belong to a L2VPN. There are two LSPs from PE1 to PE2. The LSP that goes through P1 is defined as LSP1. The LSP that goes through P2 is defined as LSP2. There are also two LSPs from PE2 to PE1. The LSP that goes through P1 is defined as LSP3. The LSP that goes through P2 is defined as LSP4.
Two PWs are established between PE1 and PE2. PW1 bears service between CE1 and CE3. PW2 bears service between CE2 and CE4. The PSN tunnel selected by PW1 is LSP1 and LSP3, which means that both directions pass through P1. The PSN tunnel selected by PW2 is LSP2 and LSP3, which means that the PE1→PE2 direction passes through P2 while the PE2→PE1 direction passes through P1. Two directions go through different P devices. At a PE, only the LSP of which the starting point is the PE can be found to be associated with PW. For instance, for PW2, it can only be determined at PE1 that PW2 is associated with LSP2. And, it can only be determined at PE2 that PE2 is associated with LSP3. Since the PEs at two ends of PW can only determine a bonding relationship between PW and LSP in a one way direction, detection results obtained at PEs of two ends may turn out to be inconsistent with each other when detecting a fault of the PW.
To better illustrate the problem, take PW2 as an example again. When a fault is detected at LSP2, since PW2 is determined, at PE1, to be associated with LSP2, the PE1 may determine that a fault occurs at PW2. However, PW2 is determined, at PE2, to be associated with LSP3. And since no fault occurs at LSP3, PE2 does not consider PW2 as faulty. Therefore, the fault detection results at PE1 and PE2 are different.